My travels have taken me all over the world and to some pretty unsavoury spots. But even I’d think twice before going to Phoenix, Arizona. Back in 2014, the city was overrun by feral chihuahuas. In packs of 15 or 20, the yapping, snarling, aggressive little creatures were roaming the streets, surrounding children on their way to school and chasing bicycles. They weren’t afraid to attack much bigger dogs — in fact, most of the time they seemed to be looking for trouble. In just one year, pest controllers reported 6,000 calls from frightened people living in a single neighbourhood, with one resident complaining: ‘It makes it hard for the kids because they get chased down all the time.’ Sounds funny? Not to me. In fact, it sounds terrifying.